AgCenter scientists study new ways to control weeds

Windrows of weeds are burned to limit how much weed seed goes back into the soil seed bank after harvest. Photo provided by Lauren Lazaro

Most farmers depend on herbicides to keep troublesome weed populations in check. But some of these unwanted plants manage to survive regardless of the chemical sprayed on them, creating a supply of seed that fuels future generations of weeds.

Lauren Lazaro, an LSU AgCenter weed scientist, is studying ways to reduce the amount of weed seed left in fields at the end of the season.

“At harvest time, if there are weeds that are present, they’ve escaped other management practices, typically herbicides,” she said. “At that point, chemicals are no longer an option for management, and we don’t want those seed going back into the soil seed bank.”

For inspiration, Lazaro is looking to Australia, where the concept of post-harvest weed seed control has taken off. She is concentrating on a practice called narrow windrow burning, which has become popular in Australia in the past decade and is beginning to catch on in the United States.

Soon after harvest, weeds are funneled into windrows and set on fire. The rows are formed using a chute attached to the back of a combine.

Farmers could build their own chutes for about $300, Lazaro said.

“It’s really straightforward, and I feel like it’s a viable option for growers in Louisiana,” she said. “It’s cost-effective. It works — it’s just if they’re willing to adopt it.”

Because the practice is still new to Louisiana, some questions remain about how it will fit into operations here. For example, it may not work as well in certain crops or in some areas of the state.

That is because of plant moisture, which can vary by crop and geography — factors Lazaro is studying. If weeds are still too “green,” they could tangle in the combine or be difficult to burn.

Lazaro also wants to find out what long-term effects the technique may have.

“If we use narrow windrow burning repeatedly, every year, what are the weeds going to do?” she said. “Are they going to shift to release their seeds earlier in the growing season? Are they going to shift more towards grasses or prostrate weeds instead of upright weeds, where the combine is able to pull them in?”

She said it’s important to remember that any management strategy can become ineffective if not employed alongside other tactics.

“This is just another tool in the toolbelt,” Lazaro said. “It’s something that should be incorporated into a management plan and used in rotation. If we overuse it, we can lose it, just like chemical weed control.”

Other researchers in the AgCenter continue to study the performance of several herbicides.

Weed scientist Donnie Miller is evaluating the Balance GT system, which includes a soybean variety that can withstand applications of the isoxaflutole-based Balance herbicide.

Miller also is studying the Xtend and Enlist systems, which use dicamba and 2,4-D, respectively. He is developing weed management strategies for Xtend and Enlist soybeans that are double-cropped with wheat. In Xtend soybeans, he is examining the feasibility of co-applying insecticides and herbicides.

Weed scientist Daniel Stephenson’s research focuses on weed control in Liberty Link and dicamba-resistant soybeans.

“We are also evaluating the effect of simulated drift of mesotrione and isoxaflutole, which will be utilized in soon-to-be commercialized herbicide-resistant soybean technology, on soybeans not tolerant to these herbicides,” he said.

Stephenson also is working to identify herbicides for controlling ragweed parthenium, a weed that has recently become a major problem in Louisiana row crops.